2                       T H E  /proc   F I L E S Y S T E M
   4/proc/sys         Terrehon Bowden <>        October 7 1999
   5                  Bodo Bauer <>
   72.4.x update      Jorge Nerin <>      November 14 2000
   8move /proc/sys    Shen Feng <>                 April 1 2009
  10Version 1.3                                              Kernel version 2.2.12
  11                                              Kernel version 2.4.0-test11-pre4
  13fixes/update part 1.1  Stefani Seibold <>       June 9 2009
  15Table of Contents
  18  0     Preface
  19  0.1   Introduction/Credits
  20  0.2   Legal Stuff
  22  1     Collecting System Information
  23  1.1   Process-Specific Subdirectories
  24  1.2   Kernel data
  25  1.3   IDE devices in /proc/ide
  26  1.4   Networking info in /proc/net
  27  1.5   SCSI info
  28  1.6   Parallel port info in /proc/parport
  29  1.7   TTY info in /proc/tty
  30  1.8   Miscellaneous kernel statistics in /proc/stat
  31  1.9   Ext4 file system parameters
  33  2     Modifying System Parameters
  35  3     Per-Process Parameters
  36  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  37                                                                score
  38  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  39  3.3   /proc/<pid>/io - Display the IO accounting fields
  40  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  41  3.5   /proc/<pid>/mountinfo - Information about mounts
  42  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  43  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  44  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  45  3.9   /proc/<pid>/map_files - Information about memory mapped files
  46  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
  47  3.11  /proc/<pid>/patch_state - Livepatch patch operation state
  49  4     Configuring procfs
  50  4.1   Mount options
  560.1 Introduction/Credits
  59This documentation is  part of a soon (or  so we hope) to be  released book on
  60the SuSE  Linux distribution. As  there is  no complete documentation  for the
  61/proc file system and we've used  many freely available sources to write these
  62chapters, it  seems only fair  to give the work  back to the  Linux community.
  63This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  64afraid it's still far from complete, but we  hope it will be useful. As far as
  65we know, it is the first 'all-in-one' document about the /proc file system. It
  66is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  67SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  68It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  69additions and patches  are welcome and will  be added to this  document if you
  70mail them to Bodo.
  72We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  73other people for help compiling this documentation. We'd also like to extend a
  74special thank  you to Andi Kleen for documentation, which we relied on heavily
  75to create  this  document,  as well as the additional information he provided.
  76Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  77and helped create a great piece of software... :)
  79If you  have  any comments, corrections or additions, please don't hesitate to
  80contact Bodo  Bauer  at  We'll  be happy to add them to this
  83The   latest   version    of   this   document   is    available   online   at
  86If  the above  direction does  not works  for you,  you could  try the  kernel
  87mailing  list  at  and/or try  to  reach  me  at
  900.2 Legal Stuff
  93We don't  guarantee  the  correctness  of this document, and if you come to us
  94complaining about  how  you  screwed  up  your  system  because  of  incorrect
  95documentation, we won't feel responsible...
 102In This Chapter
 104* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 105  ability to provide information on the running Linux system
 106* Examining /proc's structure
 107* Uncovering  various  information  about the kernel and the processes running
 108  on the system
 112The proc  file  system acts as an interface to internal data structures in the
 113kernel. It  can  be  used to obtain information about the system and to change
 114certain kernel parameters at runtime (sysctl).
 116First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 117show you how you can use /proc/sys to change settings.
 1191.1 Process-Specific Subdirectories
 122The directory  /proc  contains  (among other things) one subdirectory for each
 123process running on the system, which is named after the process ID (PID).
 125The link  self  points  to  the  process reading the file system. Each process
 126subdirectory has the entries listed in Table 1-1.
 129Table 1-1: Process specific entries in /proc
 131 File           Content
 132 clear_refs     Clears page referenced bits shown in smaps output
 133 cmdline        Command line arguments
 134 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 135 cwd            Link to the current working directory
 136 environ        Values of environment variables
 137 exe            Link to the executable of this process
 138 fd             Directory, which contains all file descriptors
 139 maps           Memory maps to executables and library files    (2.4)
 140 mem            Memory held by this process
 141 root           Link to the root directory of this process
 142 stat           Process status
 143 statm          Process memory status information
 144 status         Process status in human readable form
 145 wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
 146                symbol the task is blocked in - or "0" if not blocked.
 147 pagemap        Page table
 148 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 149 smaps          an extension based on maps, showing the memory consumption of
 150                each mapping and flags associated with it
 151 numa_maps      an extension based on maps, showing the memory locality and
 152                binding policy as well as mem usage (in pages) of each mapping.
 155For example, to get the status information of a process, all you have to do is
 156read the file /proc/PID/status:
 158  >cat /proc/self/status
 159  Name:   cat
 160  State:  R (running)
 161  Tgid:   5452
 162  Pid:    5452
 163  PPid:   743
 164  TracerPid:      0                                             (2.4)
 165  Uid:    501     501     501     501
 166  Gid:    100     100     100     100
 167  FDSize: 256
 168  Groups: 100 14 16
 169  VmPeak:     5004 kB
 170  VmSize:     5004 kB
 171  VmLck:         0 kB
 172  VmHWM:       476 kB
 173  VmRSS:       476 kB
 174  RssAnon:             352 kB
 175  RssFile:             120 kB
 176  RssShmem:              4 kB
 177  VmData:      156 kB
 178  VmStk:        88 kB
 179  VmExe:        68 kB
 180  VmLib:      1412 kB
 181  VmPTE:        20 kb
 182  VmSwap:        0 kB
 183  HugetlbPages:          0 kB
 184  CoreDumping:    0
 185  Threads:        1
 186  SigQ:   0/28578
 187  SigPnd: 0000000000000000
 188  ShdPnd: 0000000000000000
 189  SigBlk: 0000000000000000
 190  SigIgn: 0000000000000000
 191  SigCgt: 0000000000000000
 192  CapInh: 00000000fffffeff
 193  CapPrm: 0000000000000000
 194  CapEff: 0000000000000000
 195  CapBnd: ffffffffffffffff
 196  NoNewPrivs:     0
 197  Seccomp:        0
 198  voluntary_ctxt_switches:        0
 199  nonvoluntary_ctxt_switches:     1
 201This shows you nearly the same information you would get if you viewed it with
 202the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 203information.  But you get a more detailed  view of the  process by reading the
 204file /proc/PID/status. It fields are described in table 1-2.
 206The  statm  file  contains  more  detailed  information about the process
 207memory usage. Its seven fields are explained in Table 1-3.  The stat file
 208contains details information about the process itself.  Its fields are
 209explained in Table 1-4.
 211(for SMP CONFIG users)
 212For making accounting scalable, RSS related information are handled in an
 213asynchronous manner and the value may not be very precise. To see a precise
 214snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 215It's slow but very precise.
 217Table 1-2: Contents of the status files (as of 4.8)
 219 Field                       Content
 220 Name                        filename of the executable
 221 Umask                       file mode creation mask
 222 State                       state (R is running, S is sleeping, D is sleeping
 223                             in an uninterruptible wait, Z is zombie,
 224                             T is traced or stopped)
 225 Tgid                        thread group ID
 226 Ngid                        NUMA group ID (0 if none)
 227 Pid                         process id
 228 PPid                        process id of the parent process
 229 TracerPid                   PID of process tracing this process (0 if not)
 230 Uid                         Real, effective, saved set, and  file system UIDs
 231 Gid                         Real, effective, saved set, and  file system GIDs
 232 FDSize                      number of file descriptor slots currently allocated
 233 Groups                      supplementary group list
 234 NStgid                      descendant namespace thread group ID hierarchy
 235 NSpid                       descendant namespace process ID hierarchy
 236 NSpgid                      descendant namespace process group ID hierarchy
 237 NSsid                       descendant namespace session ID hierarchy
 238 VmPeak                      peak virtual memory size
 239 VmSize                      total program size
 240 VmLck                       locked memory size
 241 VmPin                       pinned memory size
 242 VmHWM                       peak resident set size ("high water mark")
 243 VmRSS                       size of memory portions. It contains the three
 244                             following parts (VmRSS = RssAnon + RssFile + RssShmem)
 245 RssAnon                     size of resident anonymous memory
 246 RssFile                     size of resident file mappings
 247 RssShmem                    size of resident shmem memory (includes SysV shm,
 248                             mapping of tmpfs and shared anonymous mappings)
 249 VmData                      size of private data segments
 250 VmStk                       size of stack segments
 251 VmExe                       size of text segment
 252 VmLib                       size of shared library code
 253 VmPTE                       size of page table entries
 254 VmSwap                      amount of swap used by anonymous private data
 255                             (shmem swap usage is not included)
 256 HugetlbPages                size of hugetlb memory portions
 257 CoreDumping                 process's memory is currently being dumped
 258                             (killing the process may lead to a corrupted core)
 259 Threads                     number of threads
 260 SigQ                        number of signals queued/max. number for queue
 261 SigPnd                      bitmap of pending signals for the thread
 262 ShdPnd                      bitmap of shared pending signals for the process
 263 SigBlk                      bitmap of blocked signals
 264 SigIgn                      bitmap of ignored signals
 265 SigCgt                      bitmap of caught signals
 266 CapInh                      bitmap of inheritable capabilities
 267 CapPrm                      bitmap of permitted capabilities
 268 CapEff                      bitmap of effective capabilities
 269 CapBnd                      bitmap of capabilities bounding set
 270 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
 271 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 272 Cpus_allowed                mask of CPUs on which this process may run
 273 Cpus_allowed_list           Same as previous, but in "list format"
 274 Mems_allowed                mask of memory nodes allowed to this process
 275 Mems_allowed_list           Same as previous, but in "list format"
 276 voluntary_ctxt_switches     number of voluntary context switches
 277 nonvoluntary_ctxt_switches  number of non voluntary context switches
 280Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 282 Field    Content
 283 size     total program size (pages)            (same as VmSize in status)
 284 resident size of memory portions (pages)       (same as VmRSS in status)
 285 shared   number of pages that are shared       (i.e. backed by a file, same
 286                                                as RssFile+RssShmem in status)
 287 trs      number of pages that are 'code'       (not including libs; broken,
 288                                                        includes data segment)
 289 lrs      number of pages of library            (always 0 on 2.6)
 290 drs      number of pages of data/stack         (including libs; broken,
 291                                                        includes library text)
 292 dt       number of dirty pages                 (always 0 on 2.6)
 296Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 298 Field          Content
 299  pid           process id
 300  tcomm         filename of the executable
 301  state         state (R is running, S is sleeping, D is sleeping in an
 302                uninterruptible wait, Z is zombie, T is traced or stopped)
 303  ppid          process id of the parent process
 304  pgrp          pgrp of the process
 305  sid           session id
 306  tty_nr        tty the process uses
 307  tty_pgrp      pgrp of the tty
 308  flags         task flags
 309  min_flt       number of minor faults
 310  cmin_flt      number of minor faults with child's
 311  maj_flt       number of major faults
 312  cmaj_flt      number of major faults with child's
 313  utime         user mode jiffies
 314  stime         kernel mode jiffies
 315  cutime        user mode jiffies with child's
 316  cstime        kernel mode jiffies with child's
 317  priority      priority level
 318  nice          nice level
 319  num_threads   number of threads
 320  it_real_value (obsolete, always 0)
 321  start_time    time the process started after system boot
 322  vsize         virtual memory size
 323  rss           resident set memory size
 324  rsslim        current limit in bytes on the rss
 325  start_code    address above which program text can run
 326  end_code      address below which program text can run
 327  start_stack   address of the start of the main process stack
 328  esp           current value of ESP
 329  eip           current value of EIP
 330  pending       bitmap of pending signals
 331  blocked       bitmap of blocked signals
 332  sigign        bitmap of ignored signals
 333  sigcatch      bitmap of caught signals
 334  0             (place holder, used to be the wchan address, use /proc/PID/wchan instead)
 335  0             (place holder)
 336  0             (place holder)
 337  exit_signal   signal to send to parent thread on exit
 338  task_cpu      which CPU the task is scheduled on
 339  rt_priority   realtime priority
 340  policy        scheduling policy (man sched_setscheduler)
 341  blkio_ticks   time spent waiting for block IO
 342  gtime         guest time of the task in jiffies
 343  cgtime        guest time of the task children in jiffies
 344  start_data    address above which program data+bss is placed
 345  end_data      address below which program data+bss is placed
 346  start_brk     address above which program heap can be expanded with brk()
 347  arg_start     address above which program command line is placed
 348  arg_end       address below which program command line is placed
 349  env_start     address above which program environment is placed
 350  env_end       address below which program environment is placed
 351  exit_code     the thread's exit_code in the form reported by the waitpid system call
 354The /proc/PID/maps file containing the currently mapped memory regions and
 355their access permissions.
 357The format is:
 359address           perms offset  dev   inode      pathname
 36108048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 36208049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3630804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 364a7cb1000-a7cb2000 ---p 00000000 00:00 0
 365a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 366a7eb2000-a7eb3000 ---p 00000000 00:00 0
 367a7eb3000-a7ed5000 rw-p 00000000 00:00 0
 368a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 369a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 370a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 371a800b000-a800e000 rw-p 00000000 00:00 0
 372a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 373a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 374a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 375a8024000-a8027000 rw-p 00000000 00:00 0
 376a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 377a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 378a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 379aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 380ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 382where "address" is the address space in the process that it occupies, "perms"
 383is a set of permissions:
 385 r = read
 386 w = write
 387 x = execute
 388 s = shared
 389 p = private (copy on write)
 391"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 392"inode" is the inode  on that device.  0 indicates that  no inode is associated
 393with the memory region, as the case would be with BSS (uninitialized data).
 394The "pathname" shows the name associated file for this mapping.  If the mapping
 395is not associated with a file:
 397 [heap]                   = the heap of the program
 398 [stack]                  = the stack of the main process
 399 [vdso]                   = the "virtual dynamic shared object",
 400                            the kernel system call handler
 402 or if empty, the mapping is anonymous.
 404The /proc/PID/smaps is an extension based on maps, showing the memory
 405consumption for each of the process's mappings. For each of mappings there
 406is a series of lines such as the following:
 40808048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 409Size:               1084 kB
 410Rss:                 892 kB
 411Pss:                 374 kB
 412Shared_Clean:        892 kB
 413Shared_Dirty:          0 kB
 414Private_Clean:         0 kB
 415Private_Dirty:         0 kB
 416Referenced:          892 kB
 417Anonymous:             0 kB
 418LazyFree:              0 kB
 419AnonHugePages:         0 kB
 420ShmemPmdMapped:        0 kB
 421Shared_Hugetlb:        0 kB
 422Private_Hugetlb:       0 kB
 423Swap:                  0 kB
 424SwapPss:               0 kB
 425KernelPageSize:        4 kB
 426MMUPageSize:           4 kB
 427Locked:                0 kB
 428VmFlags: rd ex mr mw me dw
 430the first of these lines shows the same information as is displayed for the
 431mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 432(size), the amount of the mapping that is currently resident in RAM (RSS), the
 433process' proportional share of this mapping (PSS), the number of clean and
 434dirty private pages in the mapping.
 436The "proportional set size" (PSS) of a process is the count of pages it has
 437in memory, where each page is divided by the number of processes sharing it.
 438So if a process has 1000 pages all to itself, and 1000 shared with one other
 439process, its PSS will be 1500.
 440Note that even a page which is part of a MAP_SHARED mapping, but has only
 441a single pte mapped, i.e.  is currently used by only one process, is accounted
 442as private and not as shared.
 443"Referenced" indicates the amount of memory currently marked as referenced or
 445"Anonymous" shows the amount of memory that does not belong to any file.  Even
 446a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 447and a page is modified, the file page is replaced by a private anonymous copy.
 448"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
 449The memory isn't freed immediately with madvise(). It's freed in memory
 450pressure if the memory is clean. Please note that the printed value might
 451be lower than the real value due to optimizations used in the current
 452implementation. If this is not desirable please file a bug report.
 453"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
 454"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
 455huge pages.
 456"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
 457hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
 458reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
 459"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
 460For shmem mappings, "Swap" includes also the size of the mapped (and not
 461replaced by copy-on-write) part of the underlying shmem object out on swap.
 462"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
 463does not take into account swapped out page of underlying shmem objects.
 464"Locked" indicates whether the mapping is locked in memory or not.
 466"VmFlags" field deserves a separate description. This member represents the kernel
 467flags associated with the particular virtual memory area in two letter encoded
 468manner. The codes are the following:
 469    rd  - readable
 470    wr  - writeable
 471    ex  - executable
 472    sh  - shared
 473    mr  - may read
 474    mw  - may write
 475    me  - may execute
 476    ms  - may share
 477    gd  - stack segment growns down
 478    pf  - pure PFN range
 479    dw  - disabled write to the mapped file
 480    lo  - pages are locked in memory
 481    io  - memory mapped I/O area
 482    sr  - sequential read advise provided
 483    rr  - random read advise provided
 484    dc  - do not copy area on fork
 485    de  - do not expand area on remapping
 486    ac  - area is accountable
 487    nr  - swap space is not reserved for the area
 488    ht  - area uses huge tlb pages
 489    ar  - architecture specific flag
 490    dd  - do not include area into core dump
 491    sd  - soft-dirty flag
 492    mm  - mixed map area
 493    hg  - huge page advise flag
 494    nh  - no-huge page advise flag
 495    mg  - mergable advise flag
 497Note that there is no guarantee that every flag and associated mnemonic will
 498be present in all further kernel releases. Things get changed, the flags may
 499be vanished or the reverse -- new added.
 501This file is only present if the CONFIG_MMU kernel configuration option is
 504Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
 505output can be achieved only in the single read call).
 506This typically manifests when doing partial reads of these files while the
 507memory map is being modified.  Despite the races, we do provide the following
 5101) The mapped addresses never go backwards, which implies no two
 511   regions will ever overlap.
 5122) If there is something at a given vaddr during the entirety of the
 513   life of the smaps/maps walk, there will be some output for it.
 516The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 517bits on both physical and virtual pages associated with a process, and the
 518soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
 519To clear the bits for all the pages associated with the process
 520    > echo 1 > /proc/PID/clear_refs
 522To clear the bits for the anonymous pages associated with the process
 523    > echo 2 > /proc/PID/clear_refs
 525To clear the bits for the file mapped pages associated with the process
 526    > echo 3 > /proc/PID/clear_refs
 528To clear the soft-dirty bit
 529    > echo 4 > /proc/PID/clear_refs
 531To reset the peak resident set size ("high water mark") to the process's
 532current value:
 533    > echo 5 > /proc/PID/clear_refs
 535Any other value written to /proc/PID/clear_refs will have no effect.
 537The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 538using /proc/kpageflags and number of times a page is mapped using
 539/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 541The /proc/pid/numa_maps is an extension based on maps, showing the memory
 542locality and binding policy, as well as the memory usage (in pages) of
 543each mapping. The output follows a general format where mapping details get
 544summarized separated by blank spaces, one mapping per each file line:
 546address   policy    mapping details
 54800400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
 54900600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5503206000000 default file=/lib64/ mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
 551320621f000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5523206220000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5533206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5543206800000 default file=/lib64/ mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
 555320698b000 default file=/lib64/
 5563206b8a000 default file=/lib64/ anon=2 dirty=2 N3=2 kernelpagesize_kB=4
 5573206b8e000 default file=/lib64/ anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 5583206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
 5597f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 5607f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
 5617f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
 5627fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 5637fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
 566"address" is the starting address for the mapping;
 567"policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
 568"mapping details" summarizes mapping data such as mapping type, page usage counters,
 569node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
 570size, in KB, that is backing the mapping up.
 5721.2 Kernel data
 575Similar to  the  process entries, the kernel data files give information about
 576the running kernel. The files used to obtain this information are contained in
 577/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 578system. It  depends  on the kernel configuration and the loaded modules, which
 579files are there, and which are missing.
 581Table 1-5: Kernel info in /proc
 583 File        Content                                           
 584 apm         Advanced power management info                    
 585 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 586 bus         Directory containing bus specific information     
 587 cmdline     Kernel command line                               
 588 cpuinfo     Info about the CPU                                
 589 devices     Available devices (block and character)           
 590 dma         Used DMS channels                                 
 591 filesystems Supported filesystems                             
 592 driver      Various drivers grouped here, currently rtc (2.4)
 593 execdomains Execdomains, related to security                   (2.4)
 594 fb          Frame Buffer devices                               (2.4)
 595 fs          File system parameters, currently nfs/exports      (2.4)
 596 ide         Directory containing info about the IDE subsystem 
 597 interrupts  Interrupt usage                                   
 598 iomem       Memory map                                         (2.4)
 599 ioports     I/O port usage                                    
 600 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 601 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 602 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 603 kmsg        Kernel messages                                   
 604 ksyms       Kernel symbol table                               
 605 loadavg     Load average of last 1, 5 & 15 minutes                
 606 locks       Kernel locks                                      
 607 meminfo     Memory info                                       
 608 misc        Miscellaneous                                     
 609 modules     List of loaded modules                            
 610 mounts      Mounted filesystems                               
 611 net         Networking info (see text)                        
 612 pagetypeinfo Additional page allocator information (see text)  (2.5)
 613 partitions  Table of partitions known to the system           
 614 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 615             decoupled by lspci                                 (2.4)
 616 rtc         Real time clock                                   
 617 scsi        SCSI info (see text)                              
 618 slabinfo    Slab pool info                                    
 619 softirqs    softirq usage
 620 stat        Overall statistics                                
 621 swaps       Swap space utilization                            
 622 sys         See chapter 2                                     
 623 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 624 tty         Info of tty drivers
 625 uptime      Wall clock since boot, combined idle time of all cpus
 626 version     Kernel version                                    
 627 video       bttv info of video resources                       (2.4)
 628 vmallocinfo Show vmalloced areas
 631You can,  for  example,  check  which interrupts are currently in use and what
 632they are used for by looking in the file /proc/interrupts:
 634  > cat /proc/interrupts 
 635             CPU0        
 636    0:    8728810          XT-PIC  timer 
 637    1:        895          XT-PIC  keyboard 
 638    2:          0          XT-PIC  cascade 
 639    3:     531695          XT-PIC  aha152x 
 640    4:    2014133          XT-PIC  serial 
 641    5:      44401          XT-PIC  pcnet_cs 
 642    8:          2          XT-PIC  rtc 
 643   11:          8          XT-PIC  i82365 
 644   12:     182918          XT-PIC  PS/2 Mouse 
 645   13:          1          XT-PIC  fpu 
 646   14:    1232265          XT-PIC  ide0 
 647   15:          7          XT-PIC  ide1 
 648  NMI:          0 
 650In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 651output of a SMP machine):
 653  > cat /proc/interrupts 
 655             CPU0       CPU1       
 656    0:    1243498    1214548    IO-APIC-edge  timer
 657    1:       8949       8958    IO-APIC-edge  keyboard
 658    2:          0          0          XT-PIC  cascade
 659    5:      11286      10161    IO-APIC-edge  soundblaster
 660    8:          1          0    IO-APIC-edge  rtc
 661    9:      27422      27407    IO-APIC-edge  3c503
 662   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 663   13:          0          0          XT-PIC  fpu
 664   14:      22491      24012    IO-APIC-edge  ide0
 665   15:       2183       2415    IO-APIC-edge  ide1
 666   17:      30564      30414   IO-APIC-level  eth0
 667   18:        177        164   IO-APIC-level  bttv
 668  NMI:    2457961    2457959 
 669  LOC:    2457882    2457881 
 670  ERR:       2155
 672NMI is incremented in this case because every timer interrupt generates a NMI
 673(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 675LOC is the local interrupt counter of the internal APIC of every CPU.
 677ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 678connects the CPUs in a SMP system. This means that an error has been detected,
 679the IO-APIC automatically retry the transmission, so it should not be a big
 680problem, but you should read the SMP-FAQ.
 682In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 683/proc/interrupts to display every IRQ vector in use by the system, not
 684just those considered 'most important'.  The new vectors are:
 686  THR -- interrupt raised when a machine check threshold counter
 687  (typically counting ECC corrected errors of memory or cache) exceeds
 688  a configurable threshold.  Only available on some systems.
 690  TRM -- a thermal event interrupt occurs when a temperature threshold
 691  has been exceeded for the CPU.  This interrupt may also be generated
 692  when the temperature drops back to normal.
 694  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 695  by some IO device before it could be fully processed by the APIC.  Hence
 696  the APIC sees the interrupt but does not know what device it came from.
 697  For this case the APIC will generate the interrupt with a IRQ vector
 698  of 0xff. This might also be generated by chipset bugs.
 700  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 701  sent from one CPU to another per the needs of the OS.  Typically,
 702  their statistics are used by kernel developers and interested users to
 703  determine the occurrence of interrupts of the given type.
 705The above IRQ vectors are displayed only when relevant.  For example,
 706the threshold vector does not exist on x86_64 platforms.  Others are
 707suppressed when the system is a uniprocessor.  As of this writing, only
 708i386 and x86_64 platforms support the new IRQ vector displays.
 710Of some interest is the introduction of the /proc/irq directory to 2.4.
 711It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 712IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 713irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 716For example 
 717  > ls /proc/irq/
 718  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 719  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 720  > ls /proc/irq/0/
 721  smp_affinity
 723smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 724IRQ, you can set it by doing:
 726  > echo 1 > /proc/irq/10/smp_affinity
 728This means that only the first CPU will handle the IRQ, but you can also echo
 7295 which means that only the first and third CPU can handle the IRQ.
 731The contents of each smp_affinity file is the same by default:
 733  > cat /proc/irq/0/smp_affinity
 734  ffffffff
 736There is an alternate interface, smp_affinity_list which allows specifying
 737a cpu range instead of a bitmask:
 739  > cat /proc/irq/0/smp_affinity_list
 740  1024-1031
 742The default_smp_affinity mask applies to all non-active IRQs, which are the
 743IRQs which have not yet been allocated/activated, and hence which lack a
 744/proc/irq/[0-9]* directory.
 746The node file on an SMP system shows the node to which the device using the IRQ
 747reports itself as being attached. This hardware locality information does not
 748include information about any possible driver locality preference.
 750prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 751profiler. Default value is ffffffff (all cpus if there are only 32 of them).
 753The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 754between all the CPUs which are allowed to handle it. As usual the kernel has
 755more info than you and does a better job than you, so the defaults are the
 756best choice for almost everyone.  [Note this applies only to those IO-APIC's
 757that support "Round Robin" interrupt distribution.]
 759There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 760The general  rule  is  that  the  contents,  or  even  the  existence of these
 761directories, depend  on your kernel configuration. If SCSI is not enabled, the
 762directory scsi  may  not  exist. The same is true with the net, which is there
 763only when networking support is present in the running kernel.
 765The slabinfo  file  gives  information  about  memory usage at the slab level.
 766Linux uses  slab  pools for memory management above page level in version 2.2.
 767Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 768directory cache, and so on).
 772> cat /proc/buddyinfo
 774Node 0, zone      DMA      0      4      5      4      4      3 ...
 775Node 0, zone   Normal      1      0      0      1    101      8 ...
 776Node 0, zone  HighMem      2      0      0      1      1      0 ...
 778External fragmentation is a problem under some workloads, and buddyinfo is a
 779useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 780clue as to how big an area you can safely allocate, or why a previous
 781allocation failed.
 783Each column represents the number of pages of a certain order which are 
 784available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 785ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 786available in ZONE_NORMAL, etc... 
 788More information relevant to external fragmentation can be found in
 791> cat /proc/pagetypeinfo
 792Page block order: 9
 793Pages per block:  512
 795Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 796Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 797Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 798Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 799Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 800Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 801Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 802Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 803Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 804Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 805Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 807Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 808Node 0, zone      DMA            2            0            5            1            0
 809Node 0, zone    DMA32           41            6          967            2            0
 811Fragmentation avoidance in the kernel works by grouping pages of different
 812migrate types into the same contiguous regions of memory called page blocks.
 813A page block is typically the size of the default hugepage size e.g. 2MB on
 814X86-64. By keeping pages grouped based on their ability to move, the kernel
 815can reclaim pages within a page block to satisfy a high-order allocation.
 817The pagetypinfo begins with information on the size of a page block. It
 818then gives the same type of information as buddyinfo except broken down
 819by migrate-type and finishes with details on how many page blocks of each
 820type exist.
 822If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 823from libhugetlbfs, one can
 824make an estimate of the likely number of huge pages that can be allocated
 825at a given point in time. All the "Movable" blocks should be allocatable
 826unless memory has been mlock()'d. Some of the Reclaimable blocks should
 827also be allocatable although a lot of filesystem metadata may have to be
 828reclaimed to achieve this.
 834Provides information about distribution and utilization of memory.  This
 835varies by architecture and compile options.  The following is from a
 83616GB PIII, which has highmem enabled.  You may not have all of these fields.
 838> cat /proc/meminfo
 840MemTotal:     16344972 kB
 841MemFree:      13634064 kB
 842MemAvailable: 14836172 kB
 843Buffers:          3656 kB
 844Cached:        1195708 kB
 845SwapCached:          0 kB
 846Active:         891636 kB
 847Inactive:      1077224 kB
 848HighTotal:    15597528 kB
 849HighFree:     13629632 kB
 850LowTotal:       747444 kB
 851LowFree:          4432 kB
 852SwapTotal:           0 kB
 853SwapFree:            0 kB
 854Dirty:             968 kB
 855Writeback:           0 kB
 856AnonPages:      861800 kB
 857Mapped:         280372 kB
 858Shmem:             644 kB
 859Slab:           284364 kB
 860SReclaimable:   159856 kB
 861SUnreclaim:     124508 kB
 862PageTables:      24448 kB
 863NFS_Unstable:        0 kB
 864Bounce:              0 kB
 865WritebackTmp:        0 kB
 866CommitLimit:   7669796 kB
 867Committed_AS:   100056 kB
 868VmallocTotal:   112216 kB
 869VmallocUsed:       428 kB
 870VmallocChunk:   111088 kB
 871AnonHugePages:   49152 kB
 872ShmemHugePages:      0 kB
 873ShmemPmdMapped:      0 kB
 876    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 877              bits and the kernel binary code)
 878     MemFree: The sum of LowFree+HighFree
 879MemAvailable: An estimate of how much memory is available for starting new
 880              applications, without swapping. Calculated from MemFree,
 881              SReclaimable, the size of the file LRU lists, and the low
 882              watermarks in each zone.
 883              The estimate takes into account that the system needs some
 884              page cache to function well, and that not all reclaimable
 885              slab will be reclaimable, due to items being in use. The
 886              impact of those factors will vary from system to system.
 887     Buffers: Relatively temporary storage for raw disk blocks
 888              shouldn't get tremendously large (20MB or so)
 889      Cached: in-memory cache for files read from the disk (the
 890              pagecache).  Doesn't include SwapCached
 891  SwapCached: Memory that once was swapped out, is swapped back in but
 892              still also is in the swapfile (if memory is needed it
 893              doesn't need to be swapped out AGAIN because it is already
 894              in the swapfile. This saves I/O)
 895      Active: Memory that has been used more recently and usually not
 896              reclaimed unless absolutely necessary.
 897    Inactive: Memory which has been less recently used.  It is more
 898              eligible to be reclaimed for other purposes
 899   HighTotal:
 900    HighFree: Highmem is all memory above ~860MB of physical memory
 901              Highmem areas are for use by userspace programs, or
 902              for the pagecache.  The kernel must use tricks to access
 903              this memory, making it slower to access than lowmem.
 904    LowTotal:
 905     LowFree: Lowmem is memory which can be used for everything that
 906              highmem can be used for, but it is also available for the
 907              kernel's use for its own data structures.  Among many
 908              other things, it is where everything from the Slab is
 909              allocated.  Bad things happen when you're out of lowmem.
 910   SwapTotal: total amount of swap space available
 911    SwapFree: Memory which has been evicted from RAM, and is temporarily
 912              on the disk
 913       Dirty: Memory which is waiting to get written back to the disk
 914   Writeback: Memory which is actively being written back to the disk
 915   AnonPages: Non-file backed pages mapped into userspace page tables
 916AnonHugePages: Non-file backed huge pages mapped into userspace page tables
 917      Mapped: files which have been mmaped, such as libraries
 918       Shmem: Total memory used by shared memory (shmem) and tmpfs
 919ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
 920              with huge pages
 921ShmemPmdMapped: Shared memory mapped into userspace with huge pages
 922        Slab: in-kernel data structures cache
 923SReclaimable: Part of Slab, that might be reclaimed, such as caches
 924  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 925  PageTables: amount of memory dedicated to the lowest level of page
 926              tables.
 927NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 928              storage
 929      Bounce: Memory used for block device "bounce buffers"
 930WritebackTmp: Memory used by FUSE for temporary writeback buffers
 931 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 932              this is the total amount of  memory currently available to
 933              be allocated on the system. This limit is only adhered to
 934              if strict overcommit accounting is enabled (mode 2 in
 935              'vm.overcommit_memory').
 936              The CommitLimit is calculated with the following formula:
 937              CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
 938                             overcommit_ratio / 100 + [total swap pages]
 939              For example, on a system with 1G of physical RAM and 7G
 940              of swap with a `vm.overcommit_ratio` of 30 it would
 941              yield a CommitLimit of 7.3G.
 942              For more details, see the memory overcommit documentation
 943              in vm/overcommit-accounting.
 944Committed_AS: The amount of memory presently allocated on the system.
 945              The committed memory is a sum of all of the memory which
 946              has been allocated by processes, even if it has not been
 947              "used" by them as of yet. A process which malloc()'s 1G
 948              of memory, but only touches 300M of it will show up as
 949              using 1G. This 1G is memory which has been "committed" to
 950              by the VM and can be used at any time by the allocating
 951              application. With strict overcommit enabled on the system
 952              (mode 2 in 'vm.overcommit_memory'),allocations which would
 953              exceed the CommitLimit (detailed above) will not be permitted.
 954              This is useful if one needs to guarantee that processes will
 955              not fail due to lack of memory once that memory has been
 956              successfully allocated.
 957VmallocTotal: total size of vmalloc memory area
 958 VmallocUsed: amount of vmalloc area which is used
 959VmallocChunk: largest contiguous block of vmalloc area which is free
 965Provides information about vmalloced/vmaped areas. One line per area,
 966containing the virtual address range of the area, size in bytes,
 967caller information of the creator, and optional information depending
 968on the kind of area :
 970 pages=nr    number of pages
 971 phys=addr   if a physical address was specified
 972 ioremap     I/O mapping (ioremap() and friends)
 973 vmalloc     vmalloc() area
 974 vmap        vmap()ed pages
 975 user        VM_USERMAP area
 976 vpages      buffer for pages pointers was vmalloced (huge area)
 977 N<node>=nr  (Only on NUMA kernels)
 978             Number of pages allocated on memory node <node>
 980> cat /proc/vmallocinfo
 9810xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 982  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 9830xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 984  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 9850xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 986  phys=7fee8000 ioremap
 9870xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 988  phys=7fee7000 ioremap
 9890xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 9900xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 991  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 9920xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 993  pages=2 vmalloc N1=2
 9940xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 995  /0x130 [x_tables] pages=4 vmalloc N0=4
 9960xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 997   pages=14 vmalloc N2=14
 9980xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
 999   pages=4 vmalloc N1=4
10000xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1001   pages=2 vmalloc N1=2
10020xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1003   pages=10 vmalloc N0=10
1009Provides counts of softirq handlers serviced since boot time, for each cpu.
1011> cat /proc/softirqs
1012                CPU0       CPU1       CPU2       CPU3
1013      HI:          0          0          0          0
1014   TIMER:      27166      27120      27097      27034
1015  NET_TX:          0          0          0         17
1016  NET_RX:         42          0          0         39
1017   BLOCK:          0          0        107       1121
1018 TASKLET:          0          0          0        290
1019   SCHED:      27035      26983      26971      26746
1020 HRTIMER:          0          0          0          0
1021     RCU:       1678       1769       2178       2250
10241.3 IDE devices in /proc/ide
1027The subdirectory /proc/ide contains information about all IDE devices of which
1028the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1029file drivers  and a link for each IDE device, pointing to the device directory
1030in the controller specific subtree.
1032The file  drivers  contains general information about the drivers used for the
1033IDE devices:
1035  > cat /proc/ide/drivers
1036  ide-cdrom version 4.53
1037  ide-disk version 1.08
1039More detailed  information  can  be  found  in  the  controller  specific
1040subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1041directories contains the files shown in table 1-6.
1044Table 1-6: IDE controller info in  /proc/ide/ide?
1046 File    Content                                 
1047 channel IDE channel (0 or 1)                    
1048 config  Configuration (only for PCI/IDE bridge) 
1049 mate    Mate name                               
1050 model   Type/Chipset of IDE controller          
1053Each device  connected  to  a  controller  has  a separate subdirectory in the
1054controllers directory.  The  files  listed in table 1-7 are contained in these
1058Table 1-7: IDE device information
1060 File             Content                                    
1061 cache            The cache                                  
1062 capacity         Capacity of the medium (in 512Byte blocks) 
1063 driver           driver and version                         
1064 geometry         physical and logical geometry              
1065 identify         device identify block                      
1066 media            media type                                 
1067 model            device identifier                          
1068 settings         device setup                               
1069 smart_thresholds IDE disk management thresholds             
1070 smart_values     IDE disk management values                 
1073The most  interesting  file is settings. This file contains a nice overview of
1074the drive parameters:
1076  # cat /proc/ide/ide0/hda/settings 
1077  name                    value           min             max             mode 
1078  ----                    -----           ---             ---             ---- 
1079  bios_cyl                526             0               65535           rw 
1080  bios_head               255             0               255             rw 
1081  bios_sect               63              0               63              rw 
1082  breada_readahead        4               0               127             rw 
1083  bswap                   0               0               1               r 
1084  file_readahead          72              0               2097151         rw 
1085  io_32bit                0               0               3               rw 
1086  keepsettings            0               0               1               rw 
1087  max_kb_per_request      122             1               127             rw 
1088  multcount               0               0               8               rw 
1089  nice1                   1               0               1               rw 
1090  nowerr                  0               0               1               rw 
1091  pio_mode                write-only      0               255             w 
1092  slow                    0               0               1               rw 
1093  unmaskirq               0               0               1               rw 
1094  using_dma               0               0               1               rw 
10971.4 Networking info in /proc/net
1100The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1101additional values  you  get  for  IP  version 6 if you configure the kernel to
1102support this. Table 1-9 lists the files and their meaning.
1105Table 1-8: IPv6 info in /proc/net
1107 File       Content                                               
1108 udp6       UDP sockets (IPv6)                                    
1109 tcp6       TCP sockets (IPv6)                                    
1110 raw6       Raw device statistics (IPv6)                          
1111 igmp6      IP multicast addresses, which this host joined (IPv6) 
1112 if_inet6   List of IPv6 interface addresses                      
1113 ipv6_route Kernel routing table for IPv6                         
1114 rt6_stats  Global IPv6 routing tables statistics                 
1115 sockstat6  Socket statistics (IPv6)                              
1116 snmp6      Snmp data (IPv6)                                      
1120Table 1-9: Network info in /proc/net
1122 File          Content                                                         
1123 arp           Kernel  ARP table                                               
1124 dev           network devices with statistics                                 
1125 dev_mcast     the Layer2 multicast groups a device is listening too
1126               (interface index, label, number of references, number of bound
1127               addresses). 
1128 dev_stat      network device status                                           
1129 ip_fwchains   Firewall chain linkage                                          
1130 ip_fwnames    Firewall chain names                                            
1131 ip_masq       Directory containing the masquerading tables                    
1132 ip_masquerade Major masquerading table                                        
1133 netstat       Network statistics                                              
1134 raw           raw device statistics                                           
1135 route         Kernel routing table                                            
1136 rpc           Directory containing rpc info                                   
1137 rt_cache      Routing cache                                                   
1138 snmp          SNMP data                                                       
1139 sockstat      Socket statistics                                               
1140 tcp           TCP  sockets                                                    
1141 udp           UDP sockets                                                     
1142 unix          UNIX domain sockets                                             
1143 wireless      Wireless interface data (Wavelan etc)                           
1144 igmp          IP multicast addresses, which this host joined                  
1145 psched        Global packet scheduler parameters.                             
1146 netlink       List of PF_NETLINK sockets                                      
1147 ip_mr_vifs    List of multicast virtual interfaces                            
1148 ip_mr_cache   List of multicast routing cache                                 
1151You can  use  this  information  to see which network devices are available in
1152your system and how much traffic was routed over those devices:
1154  > cat /proc/net/dev 
1155  Inter-|Receive                                                   |[... 
1156   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1157      lo:  908188   5596     0    0    0     0          0         0 [...         
1158    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1159    eth0:  614530   7085     0    0    0     0          0         1 [... 
1161  ...] Transmit 
1162  ...] bytes    packets errs drop fifo colls carrier compressed 
1163  ...]  908188     5596    0    0    0     0       0          0 
1164  ...] 1375103    17405    0    0    0     0       0          0 
1165  ...] 1703981     5535    0    0    0     3       0          0 
1167In addition, each Channel Bond interface has its own directory.  For
1168example, the bond0 device will have a directory called /proc/net/bond0/.
1169It will contain information that is specific to that bond, such as the
1170current slaves of the bond, the link status of the slaves, and how
1171many times the slaves link has failed.
11731.5 SCSI info
1176If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1177named after  the driver for this adapter in /proc/scsi. You'll also see a list
1178of all recognized SCSI devices in /proc/scsi:
1180  >cat /proc/scsi/scsi 
1181  Attached devices: 
1182  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1183    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1184    Type:   Direct-Access                    ANSI SCSI revision: 03 
1185  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1186    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1187    Type:   CD-ROM                           ANSI SCSI revision: 02 
1190The directory  named  after  the driver has one file for each adapter found in
1191the system.  These  files  contain information about the controller, including
1192the used  IRQ  and  the  IO  address range. The amount of information shown is
1193dependent on  the adapter you use. The example shows the output for an Adaptec
1194AHA-2940 SCSI adapter:
1196  > cat /proc/scsi/aic7xxx/0 
1198  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1199  Compile Options: 
1200    TCQ Enabled By Default : Disabled 
1201    AIC7XXX_PROC_STATS     : Disabled 
1202    AIC7XXX_RESET_DELAY    : 5 
1203  Adapter Configuration: 
1204             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1205                             Ultra Wide Controller 
1206      PCI MMAPed I/O Base: 0xeb001000 
1207   Adapter SEEPROM Config: SEEPROM found and used. 
1208        Adaptec SCSI BIOS: Enabled 
1209                      IRQ: 10 
1210                     SCBs: Active 0, Max Active 2, 
1211                           Allocated 15, HW 16, Page 255 
1212               Interrupts: 160328 
1213        BIOS Control Word: 0x18b6 
1214     Adapter Control Word: 0x005b 
1215     Extended Translation: Enabled 
1216  Disconnect Enable Flags: 0xffff 
1217       Ultra Enable Flags: 0x0001 
1218   Tag Queue Enable Flags: 0x0000 
1219  Ordered Queue Tag Flags: 0x0000 
1220  Default Tag Queue Depth: 8 
1221      Tagged Queue By Device array for aic7xxx host instance 0: 
1222        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1223      Actual queue depth per device for aic7xxx host instance 0: 
1224        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1225  Statistics: 
1226  (scsi0:0:0:0) 
1227    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1228    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1229    Total transfers 160151 (74577 reads and 85574 writes) 
1230  (scsi0:0:6:0) 
1231    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1232    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1233    Total transfers 0 (0 reads and 0 writes) 
12361.6 Parallel port info in /proc/parport
1239The directory  /proc/parport  contains information about the parallel ports of
1240your system.  It  has  one  subdirectory  for  each port, named after the port
1241number (0,1,2,...).
1243These directories contain the four files shown in Table 1-10.
1246Table 1-10: Files in /proc/parport
1248 File      Content                                                             
1249 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1250 devices   list of the device drivers using that port. A + will appear by the
1251           name of the device currently using the port (it might not appear
1252           against any). 
1253 hardware  Parallel port's base address, IRQ line and DMA channel.             
1254 irq       IRQ that parport is using for that port. This is in a separate
1255           file to allow you to alter it by writing a new value in (IRQ
1256           number or none). 
12591.7 TTY info in /proc/tty
1262Information about  the  available  and actually used tty's can be found in the
1263directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1264this directory, as shown in Table 1-11.
1267Table 1-11: Files in /proc/tty
1269 File          Content                                        
1270 drivers       list of drivers and their usage                
1271 ldiscs        registered line disciplines                    
1272 driver/serial usage statistic and status of single tty lines 
1275To see  which  tty's  are  currently in use, you can simply look into the file
1278  > cat /proc/tty/drivers 
1279  pty_slave            /dev/pts      136   0-255 pty:slave 
1280  pty_master           /dev/ptm      128   0-255 pty:master 
1281  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1282  pty_master           /dev/pty        2   0-255 pty:master 
1283  serial               /dev/cua        5   64-67 serial:callout 
1284  serial               /dev/ttyS       4   64-67 serial 
1285  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1286  /dev/ptmx            /dev/ptmx       5       2 system 
1287  /dev/console         /dev/console    5       1 system:console 
1288  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1289  unknown              /dev/tty        4    1-63 console 
12921.8 Miscellaneous kernel statistics in /proc/stat
1295Various pieces   of  information about  kernel activity  are  available in the
1296/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1297since the system first booted.  For a quick look, simply cat the file:
1299  > cat /proc/stat
1300  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1301  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1302  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1303  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1304  ctxt 1990473
1305  btime 1062191376
1306  processes 2915
1307  procs_running 1
1308  procs_blocked 0
1309  softirq 183433 0 21755 12 39 1137 231 21459 2263
1311The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1312lines.  These numbers identify the amount of time the CPU has spent performing
1313different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1314second).  The meanings of the columns are as follows, from left to right:
1316- user: normal processes executing in user mode
1317- nice: niced processes executing in user mode
1318- system: processes executing in kernel mode
1319- idle: twiddling thumbs
1320- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1321  are several problems:
1322  1. Cpu will not wait for I/O to complete, iowait is the time that a task is
1323     waiting for I/O to complete. When cpu goes into idle state for
1324     outstanding task io, another task will be scheduled on this CPU.
1325  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1326     on any CPU, so the iowait of each CPU is difficult to calculate.
1327  3. The value of iowait field in /proc/stat will decrease in certain
1328     conditions.
1329  So, the iowait is not reliable by reading from /proc/stat.
1330- irq: servicing interrupts
1331- softirq: servicing softirqs
1332- steal: involuntary wait
1333- guest: running a normal guest
1334- guest_nice: running a niced guest
1336The "intr" line gives counts of interrupts  serviced since boot time, for each
1337of the  possible system interrupts.   The first  column  is the  total of  all
1338interrupts serviced  including  unnumbered  architecture specific  interrupts;
1339each  subsequent column is the  total for that particular numbered interrupt.
1340Unnumbered interrupts are not shown, only summed into the total.
1342The "ctxt" line gives the total number of context switches across all CPUs.
1344The "btime" line gives  the time at which the  system booted, in seconds since
1345the Unix epoch.
1347The "processes" line gives the number  of processes and threads created, which
1348includes (but  is not limited  to) those  created by  calls to the  fork() and
1349clone() system calls.
1351The "procs_running" line gives the total number of threads that are
1352running or ready to run (i.e., the total number of runnable threads).
1354The   "procs_blocked" line gives  the  number of  processes currently blocked,
1355waiting for I/O to complete.
1357The "softirq" line gives counts of softirqs serviced since boot time, for each
1358of the possible system softirqs. The first column is the total of all
1359softirqs serviced; each subsequent column is the total for that particular
13631.9 Ext4 file system parameters
1366Information about mounted ext4 file systems can be found in
1367/proc/fs/ext4.  Each mounted filesystem will have a directory in
1368/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1369/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1370in Table 1-12, below.
1372Table 1-12: Files in /proc/fs/ext4/<devname>
1374 File            Content                                        
1375 mb_groups       details of multiblock allocator buddy cache of free blocks
13782.0 /proc/consoles
1380Shows registered system console lines.
1382To see which character device lines are currently used for the system console
1383/dev/console, you may simply look into the file /proc/consoles:
1385  > cat /proc/consoles
1386  tty0                 -WU (ECp)       4:7
1387  ttyS0                -W- (Ep)        4:64
1389The columns are:
1391  device               name of the device
1392  operations           R = can do read operations
1393                       W = can do write operations
1394                       U = can do unblank
1395  flags                E = it is enabled
1396                       C = it is preferred console
1397                       B = it is primary boot console
1398                       p = it is used for printk buffer
1399                       b = it is not a TTY but a Braille device
1400                       a = it is safe to use when cpu is offline
1401  major:minor          major and minor number of the device separated by a colon
1406The /proc file system serves information about the running system. It not only
1407allows access to process data but also allows you to request the kernel status
1408by reading files in the hierarchy.
1410The directory  structure  of /proc reflects the types of information and makes
1411it easy, if not obvious, where to look for specific data.
1419In This Chapter
1421* Modifying kernel parameters by writing into files found in /proc/sys
1422* Exploring the files which modify certain parameters
1423* Review of the /proc/sys file tree
1427A very  interesting part of /proc is the directory /proc/sys. This is not only
1428a source  of  information,  it also allows you to change parameters within the
1429kernel. Be  very  careful  when attempting this. You can optimize your system,
1430but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1431production system.  Set  up  a  development machine and test to make sure that
1432everything works  the  way  you want it to. You may have no alternative but to
1433reboot the machine once an error has been made.
1435To change  a  value,  simply  echo  the new value into the file. An example is
1436given below  in the section on the file system data. You need to be root to do
1437this. You  can  create  your  own  boot script to perform this every time your
1438system boots.
1440The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1441general things  in  the operation of the Linux kernel. Since some of the files
1442can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1443documentation and  source  before actually making adjustments. In any case, be
1444very careful  when  writing  to  any  of these files. The entries in /proc may
1445change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1446review the kernel documentation in the directory /usr/src/linux/Documentation.
1447This chapter  is  heavily  based  on the documentation included in the pre 2.2
1448kernels, and became part of it in version 2.2.1 of the Linux kernel.
1450Please see: Documentation/sysctl/ directory for descriptions of these
1456Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1457need to  recompile  the kernel, or even to reboot the system. The files in the
1458/proc/sys tree  can  not only be read, but also modified. You can use the echo
1459command to write value into these files, thereby changing the default settings
1460of the kernel.
14673.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1470These file can be used to adjust the badness heuristic used to select which
1471process gets killed in out of memory conditions.
1473The badness heuristic assigns a value to each candidate task ranging from 0
1474(never kill) to 1000 (always kill) to determine which process is targeted.  The
1475units are roughly a proportion along that range of allowed memory the process
1476may allocate from based on an estimation of its current memory and swap use.
1477For example, if a task is using all allowed memory, its badness score will be
14781000.  If it is using half of its allowed memory, its score will be 500.
1480There is an additional factor included in the badness score: the current memory
1481and swap usage is discounted by 3% for root processes.
1483The amount of "allowed" memory depends on the context in which the oom killer
1484was called.  If it is due to the memory assigned to the allocating task's cpuset
1485being exhausted, the allowed memory represents the set of mems assigned to that
1486cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1487memory represents the set of mempolicy nodes.  If it is due to a memory
1488limit (or swap limit) being reached, the allowed memory is that configured
1489limit.  Finally, if it is due to the entire system being out of memory, the
1490allowed memory represents all allocatable resources.
1492The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1493is used to determine which task to kill.  Acceptable values range from -1000
1494(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1495polarize the preference for oom killing either by always preferring a certain
1496task or completely disabling it.  The lowest possible value, -1000, is
1497equivalent to disabling oom killing entirely for that task since it will always
1498report a badness score of 0.
1500Consequently, it is very simple for userspace to define the amount of memory to
1501consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1502example, is roughly equivalent to allowing the remainder of tasks sharing the
1503same system, cpuset, mempolicy, or memory controller resources to use at least
150450% more memory.  A value of -500, on the other hand, would be roughly
1505equivalent to discounting 50% of the task's allowed memory from being considered
1506as scoring against the task.
1508For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1509be used to tune the badness score.  Its acceptable values range from -16
1510(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1511(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1512scaled linearly with /proc/<pid>/oom_score_adj.
1514The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1515value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1516requires CAP_SYS_RESOURCE.
1518Caveat: when a parent task is selected, the oom killer will sacrifice any first
1519generation children with separate address spaces instead, if possible.  This
1520avoids servers and important system daemons from being killed and loses the
1521minimal amount of work.
15243.2 /proc/<pid>/oom_score - Display current oom-killer score
1527This file can be used to check the current score used by the oom-killer is for
1528any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1529process should be killed in an out-of-memory situation.
15323.3  /proc/<pid>/io - Display the IO accounting fields
1535This file contains IO statistics for each running process
1540test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1541[1] 3828
1543test:/tmp # cat /proc/3828/io
1544rchar: 323934931
1545wchar: 323929600
1546syscr: 632687
1547syscw: 632675
1548read_bytes: 0
1549write_bytes: 323932160
1550cancelled_write_bytes: 0
1559I/O counter: chars read
1560The number of bytes which this task has caused to be read from storage. This
1561is simply the sum of bytes which this process passed to read() and pread().
1562It includes things like tty IO and it is unaffected by whether or not actual
1563physical disk IO was required (the read might have been satisfied from
1570I/O counter: chars written
1571The number of bytes which this task has caused, or shall cause to be written
1572to disk. Similar caveats apply here as with rchar.
1578I/O counter: read syscalls
1579Attempt to count the number of read I/O operations, i.e. syscalls like read()
1580and pread().
1586I/O counter: write syscalls
1587Attempt to count the number of write I/O operations, i.e. syscalls like
1588write() and pwrite().
1594I/O counter: bytes read
1595Attempt to count the number of bytes which this process really did cause to
1596be fetched from the storage layer. Done at the submit_bio() level, so it is
1597accurate for block-backed filesystems. <please add status regarding NFS and
1598CIFS at a later time>
1604I/O counter: bytes written
1605Attempt to count the number of bytes which this process caused to be sent to
1606the storage layer. This is done at page-dirtying time.
1612The big inaccuracy here is truncate. If a process writes 1MB to a file and
1613then deletes the file, it will in fact perform no writeout. But it will have
1614been accounted as having caused 1MB of write.
1615In other words: The number of bytes which this process caused to not happen,
1616by truncating pagecache. A task can cause "negative" IO too. If this task
1617truncates some dirty pagecache, some IO which another task has been accounted
1618for (in its write_bytes) will not be happening. We _could_ just subtract that
1619from the truncating task's write_bytes, but there is information loss in doing
1626At its current implementation state, this is a bit racy on 32-bit machines: if
1627process A reads process B's /proc/pid/io while process B is updating one of
1628those 64-bit counters, process A could see an intermediate result.
1631More information about this can be found within the taskstats documentation in
16343.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1636When a process is dumped, all anonymous memory is written to a core file as
1637long as the size of the core file isn't limited. But sometimes we don't want
1638to dump some memory segments, for example, huge shared memory or DAX.
1639Conversely, sometimes we want to save file-backed memory segments into a core
1640file, not only the individual files.
1642/proc/<pid>/coredump_filter allows you to customize which memory segments
1643will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1644of memory types. If a bit of the bitmask is set, memory segments of the
1645corresponding memory type are dumped, otherwise they are not dumped.
1647The following 9 memory types are supported:
1648  - (bit 0) anonymous private memory
1649  - (bit 1) anonymous shared memory
1650  - (bit 2) file-backed private memory
1651  - (bit 3) file-backed shared memory
1652  - (bit 4) ELF header pages in file-backed private memory areas (it is
1653            effective only if the bit 2 is cleared)
1654  - (bit 5) hugetlb private memory
1655  - (bit 6) hugetlb shared memory
1656  - (bit 7) DAX private memory
1657  - (bit 8) DAX shared memory
1659  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1660  are always dumped regardless of the bitmask status.
1662  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1663  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1665The default value of coredump_filter is 0x33; this means all anonymous memory
1666segments, ELF header pages and hugetlb private memory are dumped.
1668If you don't want to dump all shared memory segments attached to pid 1234,
1669write 0x31 to the process's proc file.
1671  $ echo 0x31 > /proc/1234/coredump_filter
1673When a new process is created, the process inherits the bitmask status from its
1674parent. It is useful to set up coredump_filter before the program runs.
1675For example:
1677  $ echo 0x7 > /proc/self/coredump_filter
1678  $ ./some_program
16803.5     /proc/<pid>/mountinfo - Information about mounts
1683This file contains lines of the form:
168536 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1686(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1688(1) mount ID:  unique identifier of the mount (may be reused after umount)
1689(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1690(3) major:minor:  value of st_dev for files on filesystem
1691(4) root:  root of the mount within the filesystem
1692(5) mount point:  mount point relative to the process's root
1693(6) mount options:  per mount options
1694(7) optional fields:  zero or more fields of the form "tag[:value]"
1695(8) separator:  marks the end of the optional fields
1696(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1697(10) mount source:  filesystem specific information or "none"
1698(11) super options:  per super block options
1700Parsers should ignore all unrecognised optional fields.  Currently the
1701possible optional fields are:
1703shared:X  mount is shared in peer group X
1704master:X  mount is slave to peer group X
1705propagate_from:X  mount is slave and receives propagation from peer group X (*)
1706unbindable  mount is unbindable
1708(*) X is the closest dominant peer group under the process's root.  If
1709X is the immediate master of the mount, or if there's no dominant peer
1710group under the same root, then only the "master:X" field is present
1711and not the "propagate_from:X" field.
1713For more information on mount propagation see:
1715  Documentation/filesystems/sharedsubtree.txt
17183.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1720These files provide a method to access a tasks comm value. It also allows for
1721a task to set its own or one of its thread siblings comm value. The comm value
1722is limited in size compared to the cmdline value, so writing anything longer
1723then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1724comm value.
17273.7     /proc/<pid>/task/<tid>/children - Information about task children
1729This file provides a fast way to retrieve first level children pids
1730of a task pointed by <pid>/<tid> pair. The format is a space separated
1731stream of pids.
1733Note the "first level" here -- if a child has own children they will
1734not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1735to obtain the descendants.
1737Since this interface is intended to be fast and cheap it doesn't
1738guarantee to provide precise results and some children might be
1739skipped, especially if they've exited right after we printed their
1740pids, so one need to either stop or freeze processes being inspected
1741if precise results are needed.
17443.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1746This file provides information associated with an opened file. The regular
1747files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1748represents the current offset of the opened file in decimal form [see lseek(2)
1749for details], 'flags' denotes the octal O_xxx mask the file has been
1750created with [see open(2) for details] and 'mnt_id' represents mount ID of
1751the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1752for details].
1754A typical output is
1756        pos:    0
1757        flags:  0100002
1758        mnt_id: 19
1760All locks associated with a file descriptor are shown in its fdinfo too.
1762lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1764The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1765pair provide additional information particular to the objects they represent.
1767        Eventfd files
1768        ~~~~~~~~~~~~~
1769        pos:    0
1770        flags:  04002
1771        mnt_id: 9
1772        eventfd-count:  5a
1774        where 'eventfd-count' is hex value of a counter.
1776        Signalfd files
1777        ~~~~~~~~~~~~~~
1778        pos:    0
1779        flags:  04002
1780        mnt_id: 9
1781        sigmask:        0000000000000200
1783        where 'sigmask' is hex value of the signal mask associated
1784        with a file.
1786        Epoll files
1787        ~~~~~~~~~~~
1788        pos:    0
1789        flags:  02
1790        mnt_id: 9
1791        tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1793        where 'tfd' is a target file descriptor number in decimal form,
1794        'events' is events mask being watched and the 'data' is data
1795        associated with a target [see epoll(7) for more details].
1797        The 'pos' is current offset of the target file in decimal form
1798        [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1799        where target file resides, all in hex format.
1801        Fsnotify files
1802        ~~~~~~~~~~~~~~
1803        For inotify files the format is the following
1805        pos:    0
1806        flags:  02000000
1807        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1809        where 'wd' is a watch descriptor in decimal form, ie a target file
1810        descriptor number, 'ino' and 'sdev' are inode and device where the
1811        target file resides and the 'mask' is the mask of events, all in hex
1812        form [see inotify(7) for more details].
1814        If the kernel was built with exportfs support, the path to the target
1815        file is encoded as a file handle.  The file handle is provided by three
1816        fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1817        format.
1819        If the kernel is built without exportfs support the file handle won't be
1820        printed out.
1822        If there is no inotify mark attached yet the 'inotify' line will be omitted.
1824        For fanotify files the format is
1826        pos:    0
1827        flags:  02
1828        mnt_id: 9
1829        fanotify flags:10 event-flags:0
1830        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1831        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1833        where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1834        call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1835        flags associated with mark which are tracked separately from events
1836        mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1837        mask and 'ignored_mask' is the mask of events which are to be ignored.
1838        All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1839        does provide information about flags and mask used in fanotify_mark
1840        call [see fsnotify manpage for details].
1842        While the first three lines are mandatory and always printed, the rest is
1843        optional and may be omitted if no marks created yet.
1845        Timerfd files
1846        ~~~~~~~~~~~~~
1848        pos:    0
1849        flags:  02
1850        mnt_id: 9
1851        clockid: 0
1852        ticks: 0
1853        settime flags: 01
1854        it_value: (0, 49406829)
1855        it_interval: (1, 0)
1857        where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1858        that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1859        flags in octal form been used to setup the timer [see timerfd_settime(2) for
1860        details]. 'it_value' is remaining time until the timer exiration.
1861        'it_interval' is the interval for the timer. Note the timer might be set up
1862        with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1863        still exhibits timer's remaining time.
18653.9     /proc/<pid>/map_files - Information about memory mapped files
1867This directory contains symbolic links which represent memory mapped files
1868the process is maintaining.  Example output:
1870     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/
1871     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/
1872     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/
1873     | ...
1874     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/
1875     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1877The name of a link represents the virtual memory bounds of a mapping, i.e.
1880The main purpose of the map_files is to retrieve a set of memory mapped
1881files in a fast way instead of parsing /proc/<pid>/maps or
1882/proc/<pid>/smaps, both of which contain many more records.  At the same
1883time one can open(2) mappings from the listings of two processes and
1884comparing their inode numbers to figure out which anonymous memory areas
1885are actually shared.
18873.10    /proc/<pid>/timerslack_ns - Task timerslack value
1889This file provides the value of the task's timerslack value in nanoseconds.
1890This value specifies a amount of time that normal timers may be deferred
1891in order to coalesce timers and avoid unnecessary wakeups.
1893This allows a task's interactivity vs power consumption trade off to be
1896Writing 0 to the file will set the tasks timerslack to the default value.
1898Valid values are from 0 - ULLONG_MAX
1900An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1901permissions on the task specified to change its timerslack_ns value.
19033.11    /proc/<pid>/patch_state - Livepatch patch operation state
1905When CONFIG_LIVEPATCH is enabled, this file displays the value of the
1906patch state for the task.
1908A value of '-1' indicates that no patch is in transition.
1910A value of '0' indicates that a patch is in transition and the task is
1911unpatched.  If the patch is being enabled, then the task hasn't been
1912patched yet.  If the patch is being disabled, then the task has already
1913been unpatched.
1915A value of '1' indicates that a patch is in transition and the task is
1916patched.  If the patch is being enabled, then the task has already been
1917patched.  If the patch is being disabled, then the task hasn't been
1918unpatched yet.
1922Configuring procfs
19254.1     Mount options
1928The following mount options are supported:
1930        hidepid=        Set /proc/<pid>/ access mode.
1931        gid=            Set the group authorized to learn processes information.
1933hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1936hidepid=1 means users may not access any /proc/<pid>/ directories but their
1937own.  Sensitive files like cmdline, sched*, status are now protected against
1938other users.  This makes it impossible to learn whether any user runs
1939specific program (given the program doesn't reveal itself by its behaviour).
1940As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1941poorly written programs passing sensitive information via program arguments are
1942now protected against local eavesdroppers.
1944hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1945users.  It doesn't mean that it hides a fact whether a process with a specific
1946pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1947but it hides process' uid and gid, which may be learned by stat()'ing
1948/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1949information about running processes, whether some daemon runs with elevated
1950privileges, whether other user runs some sensitive program, whether other users
1951run any program at all, etc.
1953gid= defines a group authorized to learn processes information otherwise
1954prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1955information about processes information, just add identd to this group.
1956 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.